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Oncology research with the fruit fly

Professor Owen Sansom from The Beatson Institute for Cancer Research was awarded an NC3Rs project grant in 2010. He has used the funding to study the Wnt signalling pathway in a fruit fly model of colorectal cancer, demonstrating that the fly can make a suitable alternative to mice for some studies.

Research details

Principal Investigator: Owen Sansom, Professor of Molecular OncologyOrganisation: The Beatson Institute for Cancer ResearchAward: £350,528, in 2010 over 36 monthsTitle: Using the Drosophila fly to investigate Wnt targets in vivo

Case study

Colorectal cancers are highly prevalent

Colorectal cancer is the third most common cancer worldwide. Inactivating mutations in the Adenomatous Polyposis Coli (Apc) gene occur in around 80% of colorectal cancers and appear to be associated with the very earliest stages of malignancy. APC is part of the WNT signal transduction pathway which drives the transcription of a number of key oncogenes such as Myc and Cyclin D2.

Inactivation of Apc affects the critical control point in the cell cycle, the G1 to S transition, resulting in dysregulation of cell growth in intestinal epithelial cells and the formation of intestinal polyps. It is rarely mutated in other cancers and a key challenge is to understand APC function within the intestinal epithelium and to identify why it is such a potent tumour suppressor in this tissue.

Genetic experiments for colorectal cancer research use large numbers of mice

Mouse models of colorectal cancer were first used in 1928 and since then numerous genetically altered, chemically induced and xenograft models have been used to study pathogenesis and test potential therapeutics. Complex genetic experiments, generating double knockouts and conditional mutations are increasingly required to study the role of APC and other downstream molecular targets of the WNT pathway. Such experiments use large numbers of mice to generate relatively few animals with the appropriate genotype. Compounding this, single knockout mice in the WNT pathway are often sterile or have reproductive problems (for example, Cyclin D1 mutant mice do not lactate). Moreover due to genetic redundancy, other family members in the mammalian system may mask phenotypes.

In 2010, Professor Owen Sansom, The Beatson Institute for Cancer Research, was awarded NC3Rs funding to validate the use of the fruit fly, Drosophila melanogaster, as an alternative colorectal cancer model to the mouse.

A fly model of colorectal cancer

The adult Drosophila midgut is remarkably similar to the vertebrate intestine in that the fly intestinal epithelium undergoes constant self-renewal and is replenished by stem cells. WNT signalling regulates the behaviour of Drosophila intestinal stem cells. Professor Sansom has shown previously that Apc1 deletion from the fly intestine results in a phenotype similar to the mouse with an expansion in the number of intestinal progenitors and increased proliferation and thickening of the intestinal epithelium.

With NC3Rs funding, Professor Sansom has demonstrated that the Drosophila model also has the key molecular hallmarks seen in the mouse. This includes upregulation of dMyc following loss of Apc1, and the prevention of intestinal stem cell hyperprofileration in Apc1 mutants by knocking down myc expression. Important functional roles for the JAK/STAT and SRC signalling pathways have also been identified, which had previously been suggested in mammalian cells but not characterised.

A screen to minimise the use of mice

Professor Sansom has demonstrated that the Drosophila colorectal cancer model can be used to investigate molecular targets downstream of APC, and that the fly can be used as a screen to decide which genes to test in the mouse intestine. This selective approach allows the number of mice used to be minimised. For example, Professor Sansom has shown previously in the mouse that the G protein RAC1 is required for intestinal hyperproliferation following Apc loss. To test whether RAC1 overexpression is sufficient to cause intestinal stem cell proliferation and colorectal cancer initiation, the gene was overexpressed in the fly rather than the mouse. This replaced the use of around 400 animals which would be required for the generation and characterisation of RAC1 overexpressing mice.

A similar number of mice were replaced by SRC overexpression and loss of function studies in the fly midgut. SRC is a tyrosine kinase which is amplified or mutated in human colorectal cancer although the in vivo relevance of this is unclear. The fly studies demonstrated that SRC drives intestinal stem cell proliferation and is required for tissue regeneration. Overexpression of SRC causes hyperproliferation. Based on this information it was considered that the mouse overexpression studies were unnecessary.

Extending a local reduction in mouse use to the colorectal cancer research community

The selective use of mice based on evidence derived from the fly has allowed Professor Sansom’s laboratory to use around 2,000 fewer mice a year. The model has the potential to be adopted more widely to minimise the use of mice and is already being used by groups in Edinburgh, Cambridge and New York. In 2012, Professor Sansom was awarded the CRUK Future Leaders in Cancer Research Prize in recognition of his work to understand the early changes associated with intestinal cancers.